If she has skin issues and you're breastfeeding you'll need to try eliminating different things from your diet to see what clears it up. In the mean time applying coconut oil and or lavender essential oil will help the skin heal and soothe the irritation as well as keep it from getting infected. Both have antimicrobial properties.
If she's on formula you'll need to try a different brand or variety.
You might ask in the baby health forum as well. Or peruse old threads on the subject by typing in baby eczema in the search bar on the top right of any page.